He was 74.
Williamson was hired by the Panthers to coach their wide receivers before Dom Capers was hired as the team's first head coach. Williamson coached at Carolina from its inaugural season in 1995 until his retirement 15 years later.
His top pupil at Carolina was Steve Smith, who went on to become the franchise's all-time leading receiver.
Current Panthers receivers coach Ricky Proehl played under Williamson for three seasons.
"When I think of Richard, I think of your old-school coach. He knew how to get the best out of you. He coached with tough love and got results and I had a great respect for him," Proehl said.
Receiver Muhsin Muhammad became a two-time Pro Bowl selection under Williamson's tutelage.
"Rich was instrumental in developing some of the best wide receiver talent in the NFL," Muhammad said. "He was a stickler on details and always had us prepared for our opponents. He will be dearly missed by all that worked and came into contact with him. I couldn't have asked for a better mentor, coach and friend."
During the 2000-2001 seasons, Williamson was the offensive coordinator and assistant head coach for the Panthers under George Seifert. He returned to the sole role as receivers coach in 2001.
Former Carolina general manager Marty Hurney told ESPN.com that Williamson was "one of the best men I've known."
"He was a man of integrity and a good friend," Hurney said. "Richard got it. He understood the big picture. He was old school, and I say that in the most complimentary way. He was a straight shooter, an extremely detailed coach, a teacher. He demanded the best out of his players."
Williamson attended the University of Alabama, where he played under legendary coach Bear Bryant and future Hall of Fame quarterback Joe Namath in 1962. He actually caught Namath's first touchdown pass.
Williamson began his coaching career as the receivers coach at his alma mater.
He is survived by his wife, Norma, and two children.